Electronic or communications equipment, such as computers and servers, has a plurality of jacks, in which plugs of transmission cords are inserted. This enables transmission of data or signals between the equipment and terminals, peripheral equipment, or the like. A plug of a transmission cord is usually insertable into and detachable from the jack relatively easily. If an ill-willed person removes the plug and connects his own portable terminal to the jack, or put the removed plug in a jack of his portable terminal, he may obtain an unauthorized access to the electronic or communications equipment relatively easily, and steal or destroy the information in the equipment.
In order to prevent such an unauthorized access to electronic or communications equipment, countermeasures have been taken, such as restricting physical access to a certain area around the equipment, or placing the whole equipment in a housing and locking the door of the housing.
However, it is often inconvenient to restrict physical access to the area where the electronic or communications equipment is installed, depending on the works of the persons who use the equipment. Even if the physical access to the installation area is restricted, it is difficult to preclude a possibility that an ill-willed person would remove the plug by any means and make unauthorized use of the plug or the jack.
When the whole equipment is placed in a housing, prompt rewiring of the plugs of transmission cords required at times for system modifications or the like, may be disturbed, and for equipment of certain structures, it may even be impossible to provide the housing with a door.